yagna,

'
quote
''Agnim..the first word in rik veda, in the first richa, ''Agnimile purohitham ........'' 
Agnim contains within its structure, in seed form, the full knowledge of all Laws of Nature, all evolutionary processes, and all forms and actions in the universe. A such it represents the whole value of Supreme intelligence..."......Clearly this relates to Surya, who in Jyotish represents pure consciousness, Creative Intelligence, the Self, the source of all knowledge and action. 

The superficial word meaning of Agni is "fire," 
and the Sun is the only graha that consists of fire and is illuminating with its light all the other grahas of the solar system. 

Just as Agni is the source of the whole Veda and the Vedic Literature, the Sun can be seen as the source of all activity and life forms in the solar system........maharishi 
''unquote.

if so , then what can be the significance, and what exactly is accomplished in the yagna, in which fire is lit , and offerings are made , with reciting relevant manthras??